The present invention relates to multimetal oxide materials of the formula I
(A)p(B)qxe2x80x83xe2x80x83(I),
where
A is Mo12VaX1bX2cX3dX4eX5fX6gOx,
B is X71SbhHiOy,
X1 is W, Nb, Ta, Cr and/or Ce, preferably W, Nb and/or Cr,
X2 is Cu, Ni, Co, Fe, Mn and/or Zn, preferably Cu, Ni, Co and/or Fe,
X3 is Sb and/or Bi, preferably Sb,
X4 is Li, Na, K, Rb, Cs and/or H, preferably Na and/or K,
X5 is Mg, Ca, Sr and/or Ba, preferably Ca, Sr and/or Ba,
X6 is Si, Al, Ti and/or Zr, preferably Si, Al and/or Ti,
X7 is Ni and, if required, one or more of the elements selected from the group consisting of Cu, Zn, Co, Fe, Cd, Mn, Mg, Ca, Sr and Ba,
a is 1 to 8, preferably from 2 to 6,
b is 0.2 to 5, preferably from 0.5 to 2.5,
c is 0 to 23, preferably from 0 to 4,
d is 0 to 50, preferably from 0 to 3,
e is 0 to 2, preferably from 0 to 0.3,
f is 0 to 5, preferably from 0 to 2,
g is 0 to 50, preferably from 0 to 20,
h is 0.1 to 50, preferably from 0.2 to 20, particularly preferably from 0.2 to 5,
i is 0 to 50, preferably from 0 to 20, particularly preferably from 0 to 12,
x and y are each numbers which are determined by the valency and frequency of the elements in (I) other than oxygen and
p and q are each numbers which differ from zero and whose ratio p/q is from 20:1 to 1:80, preferably from 10:1 to 1:35, particularly preferably from 2:1 to 1:3,
which contain the moiety (A)p in the form of three-dimensional regions A having the chemical composition
A: Mo12VaX1bX2cX3dX4eX5fX6gOx 
and the moiety (B)q in the form of three-dimensional regions B having the chemical composition
B: X71SbhHiOy,
the regions A, B being distributed relative to one another as in a mixture of finely divided A and finely divided B, with the proviso that, for the preparation of the multimetal oxide materials (I), at least one separately preformed oxometallate B,
X71SbhHiOy,
is present, which is obtainable by preparing a dry blend from suitable sources of the elemental constituents of the oxometallate B which contain at least a part of the antimony in oxidation stage +5 and calcining said dry blend at from 200 to  less than 600xc2x0 C., preferably from 200 to xe2x89xa6580xc2x0 C. particularly preferably from 250 to xe2x89xa6550xc2x0 C.
The present invention furthermore relates to processes for the preparation of multimetal oxide materials (I) and their use as catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid.
WO 96/27437 relates to multimetal oxide materials which contain the elements Mo, V, Cu and Sb as essential components and whose X-ray diffraction pattern has the line of strongest intensity at a 2xcex8 value of 22.2xc2x0. WO 96/27437 recommends these multimetal oxide materials as suitable catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid. Furthermore, WO 96/27437 recommends using Sb2O3 as an antimony source for the preparation of these multimetal oxide materials. Prior preparation of an Sb-containing component is not disclosed in WO 96/27437.
EP-B 235760 relates to a process for the preparation of Sb, Mo, V and/or Nb-containing multimetal oxide materials which are suitable as catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid. EP-B 235760 recommends using an antimony prepared beforehand and calcined at from 600 to 900xc2x0 C. as an antimony source for the preparation of these multimetal oxide materials.
The disadvantage of the multimetal oxide materials of the prior art is that, when they are used as catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid, their activity and the selectivity of the acrylic acid formation are not completely satisfactory.
It is an object of the present invention to provide novel multimetal oxide materials which, when used as catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid, have the disadvantages of the catalysts of the prior art to a reduced extent, if at all.
We have found that this object is achieved by the multimetal oxide materials (I) defined at the outset.
Very particularly preferred materials (I) are those whose regions A have a composition of the following formula (II)
Mo12Va,X1b,X2c,X5f,X6g,Ox,xe2x80x83xe2x80x83(II),
where
X1 is W and/or Nb,
X2 is Cu and/or Ni,
X5 is Ca and/or Sr,
X6 is Si and/or Al,
axe2x80x2 is from 2 to 6,
bxe2x80x2 is from 0.5 to 2.5,
cxe2x80x2 is from 0 to 4,
fxe2x80x2 is from 0 to 2,
gxe2x80x2 is from 0 to 2 and
xxe2x80x2 is a number which is determined by the valency and frequency of the elements in (II) other than oxygen.
It is also advantageous if at least one of the moieties (A)p, (B)q of the novel multimetal oxide materials (I) is contained in the latter in the form of three-dimensional regions having the chemical composition A or B, respectively, the maximum diameters dA and dB, respectively, of which regions (longest connecting line between two points present on the surface (interface) of the region and passing through the center of gravity of the region) are from  greater than 0 to 300 xcexcm, preferably from 0.01 to 100 xcexcm, particularly preferably from 0.05 to 50 xcexcm, very particularly preferably from 0.05 to 20 xcexcm.
Of course, the maximum diameters can also be from 0.05 to 1.0 xcexcm or from 75 to 125 xcexcm (the experimental determination of the maximum diameters permits, for example, a microstructure analysis by means of a scanning electron microscope (SEM)).
As a rule, the moiety (B)q is present in the multimetal oxide materials according to the invention essentially in crystalline form, i.e. as a rule the regions B essentially comprise small crystallites whose maximum dimension is typically from 0.05 to 20 xcexcm. However, the moiety (B)q can of course also be present in amorphous and/or crystalline form.
Particularly preferred multimetal oxide materials are those whose regions B essentially comprise crystallites which have the trirutile structure type of xcex1- and/or xcex2-copper antimonate CuSb2O6. xcex1-CuSb2O6 crystallizes in a tetragonal trirutile structure (E. -O. Giere et al., J. Solid State Chem. 131 (1997) 263-274), whereas xcex2-CuSb2O6 has a monoclinically distorted trirutile structure (A. Nakua et al., J. Solid State Chem. 91 (1991) 105-112 or reference diffraction pattern in index card 17-284 in the JCPDS-ICDD index 1989). Regions B which are also preferred are those which have the pyrochlore structure of the mineral partzite, a copper antimony copper hydroxide, having the variable composition CuySb2-x(O, OH, H2O)6-7(yxe2x89xa62.0xe2x89xa6xxe2x89xa61) (B. Mason et al., Mineral. Mag. 30 (1953) 100-112 or reference pattern in index card 7-303 of the JCPDS-ICDD index 1996).
Furthermore, the regions B may consist of crystallites which have the structure of copper antimonate Cu9Sb4O19 (S. Shimada et al., Chem. Lett. 1983, 1875-1876 or S. Shimada et al., Thermochim. Acta 133 (1988) 73-77 or reference pattern in index card 45-54 of the JCPDS-ICDD index) and/or the structure of Cu4SbO4.5 (S. Shimada et al., Thermochim. Acta 56 (1982) 73-82 or S. Shimada et al., Thermochim. Acta 133 (1988) 73-77 or reference pattern in index card 36-1106 of the JCPDS-ICDD index).
Of course, the regions B may also consist of crystallites which are a mixture of the abovementioned structures.
The novel materials (I) are obtainable in a simple manner, for example by first separately preforming oxometallates B
X71SbhHiOy,
in finely divided form as starting material 1. The oxometallates B can be prepared by preparing a preferably intimate, advantageously finely divided dry blend from suitable sources of their elemental constituents and calcining said dry blend at from 200 to 1200xc2x0 C., preferably from 200 to 850xc2x0 C., particularly preferably from 250 to  less than 600xc2x0 C., frequently is xe2x89xa6550xc2x0 C. (as a rule for from 10 minutes to several hours). All that is essential to the invention is that at least a part of the oxometallates B of the starting material 1 (referred to below as oxometallates B*) is obtainable by preparing a preferably intimate, advantageously finely divided dry blend from suitable sources of the elemental constitutents of the oxometallate B which contain at least a part of the antimony in oxidation state +5 and calcining said dry blend at from 200 to  less than 600xc2x0 C., preferably from 200 to xe2x89xa6580xc2x0 C., particularly preferably from 250 to xe2x89xa6550xc2x0 C., frequently xe2x89xa6500xc2x0 C. (as a rule for from 10 minutes to several hours). The calcination of the precursors of the oxometallates B can in general be carried out under inert gas or under a mixture of inert gas and oxygen, e.g. air, or under pure oxygen. Calcination under a reducing atmosphere is also possible. As a rule, the required calcination time decreases with increasing calcination temperature. Advantageously, the proportion of the oxometallates in the finely divided starting material 1 is at least 10, better at least 20, frequently at least 30 or at least 40, preferably at least 50, even better at least 60, particularly preferably at least 70 or at least 80, frequently at least 90 or 95, very particularly preferably 100, % by weight, based on the starting material 1.
Oxometallates B* are obtainable, for example, by the preparation methods described in detail in DE-A 24 076 77. Preferred among theseis the procedure in which antimony trioxide and/or Sb2O4 are oxidized in an aqueous medium by means of hydrogen peroxide in an amount which is equal to or greater than the stoichiometric amount at from 40 to 100xc2x0 C. to give antimony (V) oxide hydroxide hydrate, aqueous solutions and/or suspensions of suitable starting compounds of the other elemental constituents of the oxometallate B* are added before this oxidation, during this oxidation and/or after this oxidation, the resulting aqueous mixture is then dried (preferably spray-dried (inlet temperature: from 250 to 600xc2x0 C., outlet temperature: from 80 to 130xc2x0 C.)) and the intimate dry blend is then calcined as described.
In the process as described above, for example, aqueous hydrogen peroxide solutions having an H2O2 content of from 5 to 33 % by weight or more can be used. Subsequent addition of suitable starting compounds of the other elemental constituents of the oxometallate B* is advisable in particular when they are capable of catalytically decomposing the hydrogen peroxide. However, it will of course also be possible to isolate the resulting antimony (V) (V) oxide hydroxide hydrate from the aqueous medium and, for example, to dry blend it intimately with suitable finely divided starting compounds of the other elemental constituents of the oxometallate B* and then to calcine this intimate mixture as described.
It is important that the elemental sources of the oxometallates B, B* are either already oxides or are compounds that can be converted into oxides by heating in the presence or absence of oxygen.
In addition to the oxides, suitable starting compounds are therefore in particular halides, nitrates, formates, oxalates, acetates, carbonates and/or hydroxides (compounds such as NH4OH, NH4CHO2, CH3COOH, NH4CH3CO2 or ammonium oxalate, which decompose and/or can be decomposed at the latest during calcination to give compounds escaping completely in gaseous form, may additionally be incorporated). In general, for the preparation of oxometallates B, the intimate mixing of the starting compounds can be carried out in dry or wet forms. If it is effected in dry form, the starting compounds are advantageously used in the form of finely divided powders. However, the intimate mixing is preferably carried out in wet form. Usually, the starting compounds are mixed with one another in the form of an aqueous solution and/or suspension. After the end of the mixing process, the fluid material is dried and is calcined after drying. The drying is preferably carried out by spray-drying.
After calcination is complete, the oxometallates B, B* may be comminuted again (for example by wet or dry milling, for example in a ball mill or by jet milling) and the particle class having a maximum particle diameter (as a rule  greater than 0 to 300 xcexcm, usually from 0.01 to 200 xcexcm, preferably from 0.01 to 100 xcexcm, very particularly preferably from 0.05 to 20 xcexcm) which is in the maximum diameter range desired for the novel multimetal oxides (I) is separated off from the resulting powder, usually comprising essentially the spherical particles by classification to be carried out in a manner known per se (for example wet or dry sieving).
The preferred method of preparation for oxometallates B* of the formula (X71)SbhHiOy, where X7 is Ni or may be Cu and/or Zn, comprises first converting antimony trioxide and/or Sb2O4 in an aqueous medium by means of hydrogen peroxide into a preferably finely divided Sb(V) compound, e.g. antimony (V) oxide hydroxide hydrate, adding an ammoniacal aqueous solution of nickel carbonate and, if required, zinc carbonate and/or copper carbonate (which may have, for example, the composition Cu2(OH)2CO3) to the resulting aqueous suspension, drying the resulting aqueous mixture, for example spray-drying said mixture as described, and calcining the resulting powder in the manner described, if required after subsequent kneading with water and subsequent extrusion and drying.
In the case of oxometallates B differing from oxometallates B*, it proves particularly advantageous to start from an aqueous antimony trioxide suspension and to dissolve the X7 elements as nitrate and/or acetate therein, to spray-dry the resulting aqueous mixture as described and then to calcine the resulting powder as described.
According to the invention, the proportion of Ni in X7 may be xe2x89xa71 or xe2x89xa75 or xe2x89xa710 or xe2x89xa720 or xe2x89xa730 or xe2x89xa740 or xe2x89xa750, mol %. Of course, the abovementioned proportion of Ni may also be xe2x89xa760 or xe2x89xa770 or xe2x89xa780 or xe2x89xa790, mol %. However, X7 may also consist of Ni alone.
In the preparation of multimetal oxide materials (I), the starting materials 1 preformed as described can then be brought into intimate contact with suitable sources of the elemental constituents of the multimetal oxide material A,
Mo12VaX1bX2cX3dX4eX5fX6gOx,
in the desired ratio and a resulting dry blend can be calcined at from 250 to 500xc2x0 C., it being possible to carry out the calcination under inert gas (e.g. N2), a mixture of inert gas and oxygen (e.g. air), reducing gases, such as hydrocarbons (e.g. methane), aldehydes (e.g. acrolein), or ammonia, or under a mixture of O2 and reducing gases (e.g. all the abovementioned ones), as described, for example, in DE-A 43 359 73. In the case of a calcination under reducing conditions, it should be ensured that the metallic constituents are not reduced to the elements. The calcination time is as a rule a few hours and usually decreases with increasing calcination temperatures. As is generally known, all that is important with regard to the sources of the elemental constituents of the multimetal oxide material A is that they are either already oxides or compounds which can be converted into oxides by heating, at least in the presence of oxygen. In addition to the oxides, suitable starting compounds are in particular halides, nitrates, formates, oxalates, citrates, acetates, carbonates or hydroxides. Suitable starting compounds of Mo, V, W and Nb are also their oxo compounds (molybdates, vanadates, tungstates and niobates) or the acids derived from these.
The starting material 1 can be brought into intimate contact with the sources of the multimetal oxide material A (starting material 2) either in dry form or in wet form. In the latter case, it is merely necessary to ensure that the preformed multimetal oxides B, B* do not go into solution. In an aqueous medium, the latter is usually ensured at a pH which does not deviate too greatly from 7 and at xe2x89xa660xc2x0 C. or xe2x89xa640xc2x0 C., respectively. If said substances are brought into contact in wet form, drying is usually subsequently carried out to give a dry material (preferably by spray-drying). Such a dry material is automatically obtained in the course of dry blending.
Examples of possible mixing methods are therefore:
a. mixing a dry, finely divided, preformed starting material 1 with dry, finely divided starting compounds of the elemental constituents of the desired multimetal oxide A in the desired ratio in a mixer, kneader or mill;
b. preforming a finely divided multimetal oxide A by intimate mixing of suitable starting compounds or its elemental constituents (dry or wet) and then calcining the resulting intimate dry blend at from 250 to 500xc2x0 C. (with regard to the calcination time, calcination atmosphere and elemental sources, the statements made above are applicable); converting the preformed multimetal oxide A into finely divided form and mixing it with the finely divided starting material 1 in the desired ratio as in a.; in this method of mixing, final calcination of the resulting mixture is not essential;
c. stirring the required amount of preformed starting material 1 into an aqueous solution and/or suspension of starting compounds of the elemental constituents of the desired multimetal oxide A and then carrying out spray-drying; instead of the starting compounds of the elemental constituents of the desired multimetal oxide A, it is of course also possible to use a multimetal oxide A itself, already preformed according to b.
All mixing methods between a., b. and/or c. can of course also be used. The resulting intimate dry blend can then be calcined as described and then shaped to give the desired catalyst geometry, or vice versa. In principle, the calcined dry blend (or optionally uncalcined dry blend when mixing method b. is used) can however also be used in the form of a powder catalyst.
Our own investigations have shown that, on calcination of the dry blend comprising the starting material 1 and starting material 2, essentially no fusion of the constituents of the starting material 1 with those of the starting material 2 take place and the structure type or the crystallites contained in the starting material 1 is frequently essentially retained as such.
As indicated above, this opens up the possibility, after milling of the preformed starting mixture 1, of separating off the particle class having the maximum particle diameter (as a rule from  greater than 0 to 300 xcexcm, preferably from 0.01 to 100 xcexcm, particularly preferably from 0.05 to 20 xcexcm) which is in the maximum diameter range desired for the multimetal oxide material (I) from the resulting powder frequently essentially comprising spherical particles by classification to be carried out in a manner known per se (for example wet or dry sieving) and thus using said particle class in a tailor-made manner for the preparation of the desired multimetal oxide material.
When the novel multimetal oxide materials (I) are used as catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid, the shaping to give the desired catalyst geometry is preferably carried out by application to premolded inert catalyst supports, it being possible to effect application before or after the final calcination. It is possible to use the usual support materials, such as porous or nonporous aluminas, silica, thorium dioxide, zirconium dioxide, silicon carbide or silicates, such as magnesium silicate or aluminum silicate. The supports may have a regular or irregular shape, regularly shaped supports having a pronounced surface roughness, for example spheres or hollow cylinders, being preferred. Among these in turn, spheres are particularly advantageous. The use of essentially nonporous spherical steatite supports which have a rough surface and whose diameter is from 1 to 8 mm, preferably 4 to 5 mm, is particularly advantageous. The coat thickness of the active material is advantageously chosen to be in the range from 50 to 500 xcexcm, preferably from 150 to 250 xcexcm. It should be pointed out here that, for coating the supports in the preparation of such coated catalysts, the powder material to be applied is as a rule moistened and is dried again after the application, for example by means of hot air.
For the preparation of the coated catalysts, the supports are as a rule coated in a suitable rotatable container, as previously disclosed, for example, in DE-A 2909671 or EP-A 293859. As a rule, the relevant material is calcined before coating of the supports.
The coating and calcination process according to EP-A 293 859 can be used in a suitable manner known per se so that the resulting multimetal oxide active materials have a specific surface area of from 0.50 to 150 m2/g, a specific pore volume of from 0.10 to 0.90 cm3/g and a pore diameter distribution such that at least 10% of the total pore volume are accounted for in each case by the diameter ranges from 0.1 to  less than 1 xcexcm, from 1.0 to  less than 10 xcexcm and 10 xcexcm to 100 xcexcm. The pore diameter distributions stated as being preferred in EP-A 293 859 may also be established.
Of course, the novel multimetal oxide materials may also be operated as unsupported catalysts. In this respect, the intimate dry blend comprising the starting materials 1 and 2 is preferably compacted directly to give the desired catalyst geometry (for example by means of pelleting or extrusion) it being possible, if required, to add conventional assistants, e.g. graphite or stearic acid, as lubricants and/or molding assistants and reinforcing materials such as microfibers of glass, asbestos, silicon carbide or potassium titanate, and is calcined. Here too, calcination can generally be effected prior to the shaping procedure. Preferred geometries for unsupported catalysts are hollow cylinders having an external diameter and a length of 2 to 10 mm and a wall thickness of 1 to 3 mm.
The novel multimetal oxide materials are especially suitable as catalysts having high activity and selectivity (at a given conversion) for the gas-phase catalytic oxidation of acrolein to acrylic acid. The process is usually carried out using acrolein which was produced by the catalytic gas-phase oxidation of propene. As a rule, the acrolein-containing reaction gases from this propene oxidation are used without intermediate purification. Usually, the gas-phase catalytic oxidation of acrolein is carried out in tube-bundle reactors as a heterogeneous fixed-bed oxidation. Oxygen, advantageously diluted with inert gases (for example in the form of air), is used as an oxidizing agent in a manner known per se. Suitable diluent gases are, for example, N2, CO2, hydrocarbon, recycled reaction gases and/or steam. As a rule, an acrolein:oxygen:steam inert gas volume ratio of 1:(1 to 3):(0 to 20):(3 to 30), preferably 1:(1 to 3):(0.5 to 10):(7 to 18), is established in the acrolein oxidation. The reaction pressure is in general from 1 to 3 bar and the total space velocity is preferably from 1000 to 3500 l (s.t.p.)/l/h. Typical multitube fixed-bed reactors are described, for example, in DE-A 2830765, DE-A 2 201 528 or U.S. Pat. No. 3,147,084. The reaction temperature is usually chosen so that the acrolein conversion in a single pass is above 90%, preferably above 98%. Usually, reaction temperatures of from 230 to 330xc2x0 C. are required for this.
In addition to the gas-phase catalytic oxidation of acrolein to acrylic acid, the novel products are, however, also capable of catalyzing the gas-phase catalytic oxidation of other organic compounds, in particular other alkanes, alkanols, alkanals, alkenes and alkenols, preferably of 3 to 6 carbon atoms (e.g. propylene, methacrolein, tert-butanol, methyl ether of tert-butanol, isobutene, isobutane or isobutyraldehyde), to give olefinically unsaturated aldehydes and/or carboxylic acids, and the corresponding nitriles (ammoxidation, especially of propene to acrylonitrile and of isobutene or tert-butanol to methacrylonitrile). The preparation of acrolein, methacrolein and methacrylic acid may be mentioned by way of example. However, they are also suitable for the oxidative dehydrogenation of olefinic compounds.
Unless stated otherwise, the conversion, selectivity and residence time are defined as follows in this publication:                     Conversion        ⁢                  xe2x80x83                ⁢        C        ⁢                  xe2x80x83                ⁢        to        ⁢                  xe2x80x83                ⁢                  acrolein          ⁡                      (            %            )                              =                                                                                    Number                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  moles                  ⁢                                      xe2x80x83                                    ⁢                  of                                                                                                      acrolein                  ⁢                                      xe2x80x83                                    ⁢                  converted                                                                                                                          Number                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  moles                                                                                                      of                  ⁢                                      xe2x80x83                                    ⁢                  acrolein                  ⁢                                      xe2x80x83                                    ⁢                  used                                                                    xc3x97        100              ;                                                                          Selectivity                ⁢                                  xe2x80x83                                ⁢                S                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                the                            ⁢                              xe2x80x83                                                                                        acrylic              ⁢                              xe2x80x83                            ⁢              acid              ⁢                              xe2x80x83                            ⁢              formation              ⁢                              xe2x80x83                            ⁢              %                                          =                                                                                    Number                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  moles                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  acrolein                                                                                                      converted                  ⁢                                      xe2x80x83                                    ⁢                  into                  ⁢                                      xe2x80x83                                    ⁢                  acrylic                  ⁢                                      xe2x80x83                                    ⁢                  acid                                                                                                                          Total                  ⁢                                      xe2x80x83                                    ⁢                  number                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  moles                  ⁢                                      xe2x80x83                                    ⁢                  of                                                                                                      acrolein                  ⁢                                      xe2x80x83                                    ⁢                  converted                                                                    xc3x97        100              ;              Residence      ⁢              xe2x80x83            ⁢      time      ⁢              xe2x80x83            ⁢              (        sec        )              =                                                                      Empty                ⁢                                  xe2x80x83                                ⁢                reactor                ⁢                                  xe2x80x83                                ⁢                volume                ⁢                                  xe2x80x83                                ⁢                filled                                                                                        with                ⁢                                  xe2x80x83                                ⁢                catalyst                ⁢                                  xe2x80x83                                ⁢                                  (                  1                  )                                                                                                                        Sythesis                ⁢                                  xe2x80x83                                ⁢                gas                ⁢                                  xe2x80x83                                ⁢                throughput                                                                                        (                                  1                  ⁢                                                            (                      STP                      )                                        /                    h                                                  )                                                        xc3x97      3600.      